Method and transceiving device for retransmitting erroneous information units in radio links

ABSTRACT

The present invention is related to an error handling in transmission of information units in radio links and in particular it is related to an error handling using automatic repeat request (ARQ) and transmission of information units in mobile communication. To reduce the access delay of packet data services, the present invention uses different code ratings according to type II hybrid ARQ for different erroneous information units selected from a formatted block of information units before retransmission. Therefore erroneous information units of a block of information units, that have been transmitted, are selected and the set of selected erroneous information units is divided into a set of n subsets encoded with n code ratings. Advantageously, the retransmission of portions of the formatted block with different code ratings enhances the reliability of the retransmission.

[0001] The present invention is related to an error handling intransmission of information units in radio links and in particular it isrelated to an error handling using automatic repeat request (ARQ) andtransmission of information units in mobile communication.

[0002] In mobile communication, transmission is performed by using adigital modulation to impress data on carrier waves. There exists alarge variety of standardised air interfaces, such as the Global Systemfor Mobile Communication (GSM) standard specified by the EuropeanTelecommunication Standard Institute (ETSI) using time division multipleaccess (TDMA), while in the United States a number of interim standardssuch as IS-54 and IS-136 is defined.

[0003] The growing number of mobile terminal devices such as mobilephones or communicators yields a bigger demand for voice and datachannels within the system of mobile communication. The increasinginterference between neighbouring base stations and interference withother devices using radio link decreases the carrier to interference(C/I) or carrier to noise (C/N) ratio. Thus, the quality of mobile phonechannels is highly fluctuating, so that transmission of erroneousinformation or information that is being corrupted during transmissionis a very common phenomenon. The quota of erroneous units can be as highas 1% o up to 10%.

[0004] To handle the problem of large error rates, usually a channelcoding (convolutional coding can also be used other than block coding)is used to introduce a redundancy to the data stream, which allows for arecognition and a possible correction of erroneous units transmitted.The definition of such a channel coding is known to every person skilledin the art, and thus a more precise discussion is omitted from thefollowing specification. The reliability of the channel coding isdefined by the number of data bits per coded bits ν. The higher thenumber of data bits per code bits ν, the less redundancy is introducedto the data stream and the less encoded information unit is securedagainst corruption during transmission. If an erroneous unit isreceived, a retransmission of the (in type II hybrid ARQ, theretransmitted date can be not the same as the first transmission) datais necessary. Accordingly, the basic ARQ scheme provides error detectionand retransmission capabilities. If an information unit is found to becorrupted during transmission, it is discarded and a retransmission ofthe same information unit is requested.

[0005] On the other hand a fast transmission of data other than voicechannels, such as in the general packet radio service (GPRS) standard orin the upcoming universal mobile telecommunication system (UMTS)standard, is essential due to a large amount of transferred data and alimited transmission rate. The transmission rate is determined amongother factors by the reliability of the transferred data. The higher thenumber of coded bits the poorer the transmission rate. Yet, it isimportant to select from a large number of data bits per coded bits νcorresponding to the quality of the transmission link to ensure a fastand reliable transmission.

[0006] One commonly used scheme is the type II hybrid ARQ. In the typeII hybrid ARQ scheme, information is first sent with high (code rating ⅔as “higher” than ½.) code rating, i.e. little redundancy, and if oneerroneous unit is requested to be retransmitted, additional code bitswill be added for the following transmission. This enhances theefficiency of the transmission. First, a rather poor coding is used andonly if transmission fails due to erroneous units, a more reliable blockcode is used.

[0007] For example, two different types of type II hybrid ARQ schemescan be used. A set of consequent code ratings defined by the number ofdata bits per code bits ν increasing as 1→½→⅓ is used. Another one isusing a finer code rating granularity. This scheme yields a code ratingof ν: 1→⅔→½→⅖→⅓. It is appreciated by a person skilled in the art, thata fine code rating granularity results in a higher link throughput butin higher normalised packet delays as well.

[0008] Therefore, it is the object of the present invention to reducethe access delay of packet data services. According to the presentinvention, this object is achieved by using different code ratings fordifferent erroneous units selected from a formatted block of informationunits before retransmission.

[0009] Accordingly, a method for retransmitting a formatted block ofinformation units, that have been transmitted in radio links (a mainfeature of mobile communication systems, such as mobiletelecommunication systems for mobile cell phones, satellitecommunication systems, or radio relay systems) using a first coderating, is provided. It comprises the steps of selecting all erroneousunits of the block of information units, that have been transmitted,dividing the selected set of erroneous units into n disjunct subsets,selecting a set of n distinct code ratings, encoding all erroneous unitsof the i-th subset with one of the distinct code ratings, formatting ablock composed of the encoded erroneous units, and transmitting theformatted block. This method has the advantage of retransmittingdifferent portions of the formatted block with different code ratings.Usually, information units are interdependent, and if a first erroneousunit is corrupted during retransmission all consequent erroneous unitswill still be held in the buffer even if they are received correctlyafter combination.

[0010] In a preferred embodiment, the method of the present inventionfurther comprises a step of interleaving at least two information unitswhile formatting a block of the encoded erroneous units. Interleaving ispreferably performed due to a strongly correlated occurrence of biterrors during transmission.

[0011] In another preferred embodiment of the present invention, thefirst code rating is having a first number of data bits per code bits,and the elements of the set of code ratings are having each a number ofdata bits per coded bits and the first number is greater than eachnumber of data bits per coded bits of the set of code ratings. Thus, thereliability of transmission is increased while retransmitting theerroneous information units. Preferably, the selected set of erroneousunits is divided into two disjunct subsets, while one subset consists ofa first erroneous unit and the other subset consists of all othererroneous units and advantageously the first subset consisting of afirst transmitted erroneous unit is encoded using a code rating having anumber of date bits per coded bits greater than a code rating used tomodulate the second subset.

[0012] Normally, if the unit of a first code rating is received witherror, another, lower code rating will be used for retransmission. Inthe preferred embodiment present invention, all units are encoded by afirst code rating. If a set of units is received with error, the firstunit will be retransmitted with a lower code rating. All other erroneousunits will be encode by a code rating lower than the original coderating, yet not as reliable as the code rating of the first erroneousunit, so as to allow for an average delay less than in the type IIhybrid ARQ scheme known in the prior art. If errors persist afterretransmission, the remaining erroneous units will be retransmitted witha refined corresponding code rating.

[0013] Yet, according to another preferred embodiment of the presentinvention, the erroneous units are divided into subsets, such that everysubset contains one single erroneous unit. Preferably, the subsets areordered according to a timely sequence of their transmission.Advantageously, the set of code rating is ordered according to thevalues of each number of data bits per coded bits. Like in the abovementioned embodiment, not all erroneous units are retransmitted using amore reliable code rating. The reliability of transmission is adapted tothe sequence of the erroneous units, since earlier transmitted units maycause subsequent units to be hold in buffer.

[0014] According to another aspect of the present invention, a computerprogram product is provided, comprising program code means stored on acomputer readable medium for performing the method for retransmittingerroneous information units using a type II ARQ scheme. By using acomputer program for the execution of the method for retransmittingerroneous information units using a type II ARQ scheme, the method caneasily be implemented in a computer or terminal device.

[0015] According to yet another aspect of the present invention, acomputer program product is provided, comprising program code meansstored on a computer readable medium for performing the method of any ofthe claims 1 to 8 when the program product is run on a computer orterminal device.

[0016] According to still another aspect of the present invention, atransceiving device is provided, comprising means for transceivinginformation units, means for selecting erroneous units, that have beencorrupted during transmission, means for requesting a retransmission ofthe erroneous units, means for receiving a retransmission request, meansfor selectively modulating erroneous units using a set of selected coderatings, and means for formatting a block.

[0017] Since communication is always going in both directions, a devicetaking part in communication transmits as well as it receives formattedblocks of information units. It unravels a formatted block and checksevery information unit, if it is received with error or not. Thus itselects all erroneous units, that have been corrupted duringtransmission and can not be corrected by help of the redundancy of acode rating used for encoding or modulation before transmission. Iferroneous units are received, a retransmission request is send,requesting for a retransmission of those units, until no more erroneousunits are found. The same device is used on the other hand to transmitinformation units. Those information units are first encoded by a set ofselected code ratings, formatted to a block and than transmitted by thetransceiving means. If a retransmission request is received, indicatingthat a subset of the transmitted information had been received byanother transceiving device with error, those erroneous units areselected and encoded anew with a different set of code ratings, selectedaccording to the previously described method, before being formatted toa block and being retransmitted.

[0018] The transceiving device may be a terminal device, preferably amobile terminal device or it may be an access point in mobilecommunication. Examples for those transceiving devices are mobile phonesor base stations in a mobile communication system. Yet, it will beappreciated, that other transceiving devices may be thought of, such assatellites or computers and other devices, linked by wirelessconnection, such as bluetooth, infrared (IR) or radio relay systems.

[0019] According to still yet another aspect of the present invention, acommunication network is provided, comprising at least one transceivingdevice and at least one access point in communication for thetransceiving device and forming part of a network. A communicationnetwork thus consists of at least two transceiving devices, one beingthe access point in communication. Preferably, the communication networkaccording the present invention further comprises a server, where theserver is coupled to another network, and advantageously, at least onenetwork is a network in mobile communication. The network is preferablythe Internet.

[0020] A more complete appreciation of the invention and many otherattendant advantages thereof will be readily obtained, as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0021]FIG. 1 shows a schematic diagram of the method for retransmittingerroneous information units according to a preferred embodiment of thepresent invention and

[0022]FIG. 2 illustrates a communication network exchanging informationunits by radio link.

[0023] As shown in FIG. 1 a formatted block B_(init) of information unit1, 2, 3, 4, 5, 6, 7, 8, 9, 10 is received, of which four units 1, 4, 5,8 are identified as being corrupted during transmission and a correctionof these not being possible. This erroneous units 1, 4, 5, 8 areselected and in a first step I. a retransmission of these units 1, 4, 5,8 is requested. The retransmission of the erroneous units 1, 4, 5, 8 isprepared by selecting a set of corresponding code ratings R₁, R₄, R₅, R₈in step II. According to the present invention, these code ratingsdiffer from the code rating of the initial transmission by having lessdata bits per coded bits, so as to assure a more reliableretransmission. The set of coded bits may consist of code ratings havingdifferent numbers of data bits per coded bit. In any case the coderating R₁ of the first erroneous units 1 should have the lowest numberof data bits per code bits, so as to ensure that the first erroneousunit is retransmitted using the most reliable coding.

[0024] According to one preferred embodiment of the present invention,the other code ratings R₄, R₅, R₈ may be all equal concerning the numberof data bits per coded bits, thus being of similar reliability.According to another preferred embodiment of the present invention, allcode ratings R₄, R₅, R₈ differ from each other, having different numbersof data bits per code bits, so that one code rating is always havingless data bits per coded bits, i.e. being more reliable, than allconsequent code ratings. Yet it should be noted, that many differentchoices of the code ratings may be used. In a consequent third stepIII., all erroneous units 1, 4, 5, 8 are encoded with the correspondingcode ratings R₁, R₄, R₅, R₈ before being formatted to a block ofinformation units B_(retrans), which preferably may include a step ofinterleaving the erroneous units 1, 4, 5, 8, so as to handle correlatedinterference during transmission. The formatted block B_(retrans) is tobe retransmitted.

[0025]FIG. 2 illustrates a communication network according to anpreferred embodiment of the present invention, consisting of a mobileterminal device 20 being in mobile communication with an access point 22connected to a network 24 by radio link 26. The mobile terminal device20 and the access point 22 in mobile communication are exchangingformatted blocks of information units, that may be corrupted duringtransmission by radio link 26. If for example, the mobile terminaldevice 20 is receiving a formatted block of information units containingerroneous units it is selecting those units and requesting aretransmission of the erroneous units from the access point 22. Theaccess point 22 is encoding the erroneous units and formatting a blockof these encoded erroneous units according to the above described methodand retransmitting this block. Retransmission is performed until allinformation units are received without error, while every retransmissionis having a higher reliability than the preceding transmission.Transmission is performed in the same manner, if the mobile terminaldevice 20 is acting as transmitter and the access point 22 is receivingtransmitted data.

[0026] This specification contains the description of implementationsand embodiments of the present invention with the help of examples. Itwill be appreciated by a person skilled in the art, that the presentinvention is not restricted to details of the embodiments presentedabove, and that the invention can also be implemented in another formwithout deviating from the characteristics of the invention. Theembodiments presented above should be considered as illustrative, butnot restricting. Thus, the possibilities of implementing and using theinvention are only restricted by the enclosed claims. Consequently,various options of implementing the invention as determined by theclaims, including equivalent implementations, also belong to the scopeof the invention.

1. A method for retransmitting a formatted block (B_(init)) ofinformation units (1-10) that have been transmitted in radio links (26)using a first number of data bits per coded bits, comprising the stepsof: selecting all erroneous units (1, 4, 5, 8) of said block ofinformation units (1-10) that have been transmitted; dividing saidselected set of erroneous units (1, 4, 5, 8) into n disjunct subsets,wherein n is greater than or equal to 2; selecting a set of n distinctnumbers of data bits per coded bits (R₁, R₄, R₅, R₈); encoding allerroneous units of each of said subsets with a different one of saidnumbers of data bits per coded bits (R₁, R₄, R₅, R₈), wherein the numberof data bits per coded bits of the first erroneous units is the lowestof said numbers of data bits per coded bits (R₁, R₄, R₅, R₈); formattinga block (B_(retrans)) composed of said encoded erroneous units (1, 4, 5,8); and transmitting said formatted block (B_(retrans)).
 2. A methodaccording to claim 1, wherein formatting a block (B_(retrans)) of saidencoded erroneous units (1, 4, 5, 8) comprises the step of interleavingat least two of said encoded erroneous units.
 3. A method according toclaim 1, wherein said first number of data bits per coded bits isgreater than each number of data bits per coded bits out of said set ofnumbers of data bits per coded bits (R₁, R₄, R₅, R₈).
 4. A methodaccording to claim 1, with n equal to 2, wherein one subset consists ofa first erroneous unit (1) and the other subset consists of all othererroneous units (4, 5, 8).
 5. A method according to claim 4, whereinsaid first subset consisting of a first transmitted erroneous unit (1)is encoded using a number of data bits per coded bits (R₁) which issmaller than the number of data bits per coded bits (R₄, R₅, R₈) used toencode said second subset (4, 5, 8).
 6. A method according to claim 3,wherein each of said subsets contains one single erroneous unit (1, 4,5, 8).
 7. A method according to claim 1, wherein said subsets areordered according to a timely sequence of their transmission.
 8. Amethod according to claim 1, wherein the set of said numbers of databits per coded bits (R₁, R₄, R₅, R₈) is ordered according to the numbersof data bits per coded bits.
 9. A computer program product comprisingprogram code means stored on a computer readable medium for carrying outthe method of claim 1 when said program product is run on a computer ornetwork device.
 10. A computer program product comprising program code,downloadable from a server for carrying out the method of claim 1 whensaid program product is run on a computer or network device.
 11. Atransceiving device, comprising: a component for transceivinginformation units (1-10); a component for selecting erroneous units (1,4, 5, 8) that have been corrupted during transmission; a component forrequesting a retransmission of said erroneous unit (1, 4, 5, 8); acomponent for receiving a retransmission request; a component fordividing said selected set of erroneous units (1, 4, 5, 8) into ndisjunct subsets, wherein n is greater than or equal to 2; a componentfor selecting a set of n distinct numbers of data bits per coded bits(R₁, R₄, R₅, R₈); a component for selectively modulating all erroneousunits of each of said subsets with a different one of said numbers ofdata bits per coded bits (R₁, R₄, R₅, R₈), wherein the number of databits per coded bits of the first erroneous unit is the lowest of saidnumbers of data bits per coded bits (R₁, R₄, R₅, R₈); and an encodingcomponent for formatting a block (B_(retrans)) composed of said encodederroneous units (1, 4, 5, 8).
 12. A transceiving device according toclaim 11, wherein said transceiving device is a terminal device.
 13. Atransceiving device according to claim 12, wherein said transceivingdevice is a mobile terminal device (20).
 14. A transceiving deviceaccording to claim 13, wherein said transceiving device is an accesspoint (22) in mobile communication.
 15. A communication networkcomprising: at least one transceiving device (20, 22) according to claim11; and at least one access point (22) in communication for saidtransceiving device and forming part of a network (24).
 16. Acommunication network according to claim 15, further comprising aserver, characterised in that said server is coupled to another network.17. A communication network according to claim 16, wherein at least onenetwork (24) is a network in mobile communication.
 18. A communicationnetwork according to claim 16, wherein said network is the Internet.